U.S. Pat. No. Reissue 31,847, reissued Mar. 12, 1985, inventor Luckey, discloses a storage phosphor system in which a storage phosphor is exposed to an x-ray image of an object, such as the body part of a patient, to record a latent x-ray image in the storage phosphor. The latent x-ray image is read out by stimulating the storage phosphor with relatively long wavelength stimulating radiation such as red or infrared light produced by a gas or diode laser. Upon stimulation, the storage phosphor releases emitted radiation of an intermediate wavelength, such as blue light, in proportion to the quantity of x-rays that were received. To produce a signal useful in electronic image processing, the storage phosphor is scanned in a raster pattern by a laser beam deflected by an oscillating or rotating scanning mirror or by a rotating hologon. The emitted radiation from the storage phosphor is reflected by a mirror light collector and detected by one or more light detectors to produce an x-ray image signal. Typically, the storage phosphor is translated in a page or slow scan direction past the laser beam which is repeatedly deflected in a line or fast scan direction perpendicular to the page or slow scan motion of the storage phosphor to form an image signal having a matrix of pixels. The x-ray image signal can then be viewed as a visual image produced on a video monitor or other display device or as a permanent image printed out on film or paper.
In storage phosphor readers it is desirable to provide high emitted light collection efficiency in order to speed up the reading of a storage phosphor and to attain maximum reader performance. There has been proposed a storage phosphor reader having a highly efficient emitted light collector system including an array of five photodetectors (photomultiplier tubes) which receive light either directly emitted from a storage phosphor or reflected by a highly efficient specularly reflective mirror light collector. In such a storage phosphor reader, there is a need to verify that all of the photodetectors are functioning, that each of the photodetector signal channels has appropriate gain, and that the output of the several photodetectors is corrected for variations in signal output across the line scan direction. More generally, there is also a need to fit the length of the scanning beam to the dimension of the storage phosphor in the line scan direction and to locate the leading edge of the storage phosphor in the page scan direction.